1. Field of the Invention
This invention relates to a liquid crystal display.
2. Prior Art
Most liquid crystal devices are comprised of two spaced parallel substrates with liquid crystal between the substrates. Electrical conductors for the application of a selected voltage are formed on internal facing sides of the substrates. When a voltage is applied to the liquid crystal via the electrical conductors, the liquid crystal changes from a first state to a second state. Typically, in the first state, the liquid crystal is transparent, while in the second state it forms a light altering (e.g., dynamic scattering or field effect).
By placing formed electrodes in certain desired locations specific images coinciding with the formed electrode can be selectively made to appear in the liquid crystal. For example, one form of the liquid crystal display unit employs front and rear transparent substrates, and is viewed from the front substrate. The front and rear substrates and front electrodes are transparent, while the rear electrode may be reflective or transparent. In addition, the rear substrate may employ an additional layer of coating to achieve certain desired optical effects. This additional layer may be located on the external facing side of the rear substrate. When the device is used, light is directed into the front side of the display and the electrodes are energized. Various parts of the liquid crystal become light enabled (e.g. scattering) and the effect is to view enabled (e.g. scattering) portions on a contrasting or mirror-like background. There are, of course, other forms of liquid crystal display which do not employ various physical effects and which may employ the invention described herein.
The operation and construction of liquid crystal display devices, such as described above, is well known in the prior art. Two examples of such prior art are U.S. Pat. No. 3,322,485 and U.S. Pat. No. 3,612,654.
There have been numerous problems in prior art liquid crystal display devices regarding the fragmented or pad-like configuration of the contrasting (e.g. reflective) surface. This pad-like configuration has resulted in the energized segment having one contrast to certain portions of the display and another contrast as to other portions of the display. This results in poor overall contrast. This problem is solved by the present invention by creating a solid contrasting (e.g. reflective) surface on the second substrate. A further benefit is that the unpowered segments are made less visible because there is no adjacent "bare" glass to provide optical contrast.
A primary characteristic of prior art liquid crystal display devices is that both substrates are required to be perfectly aligned both in the horizontal and vertical plane. The present invention eliminates any critical alignment required between the two substrates. The present invention embodies a structure which will allow mechanical alignment assembly techniques for positioning the two substrates resulting in substantial manufacturering economics.
However, when a solid reflective surface is employed on one substrate the undesirable effect of lead illumination occurs. It is believed that the prior art solid reflective surfaces were not considered because of lead illumination, instead pads were employed. The present invention solves the problem of lead illumination by forming the leads from an opaque conductor having blending characteristic, such as having the same reflective properties as the first substrate.
Haze formation was also a problem in the prior art. Haze was created due to the molecular alignment characteristics of liquid crystal when it contacted a surface. In the present invention haze formation is reduced since the number of different surfaces the liquid crystal must contact is reduced.